(i) Field of the Invention
This invention relates generally to furnaces and particularly to cooling a motor that drives a draft inducing fan in a furnace. The invention provides for an improved method of cooling the motor that drives the inducer fan and an apparatus for practicing the method.
(ii) Description of the Related Art
Typically, a household furnace includes an inducer fan and motor that draw a flow of air through a combustion chamber and then a heat exchanger of the furnace before exhausting the combustion gases from the furnace, and a blower fan and motor that draw a flow of air into the furnace and blow the flow of air across the heat exchanger to heat the air and then deliver the heated air to the conduit system that directs the heated air through the household.
In typical prior art furnaces, the fan motor is located in the vestibule of the furnace which also houses the electronics and controls for controlling the furnace. The heat generated by the blower motor elevates the temperature within the vestibule. The elevated temperature within the vestibule can shorten the life of the electronics and controls located within the vestibule. Additionally, the excess heat generated by the motor can shorten the life of the motor itself.
Typical prior art furnace fans utilize a motor that has an auxiliary fan attached to the rotating shaft of the motor to cool the motor. The auxiliary fan forces a flow of air across the motor to dissipate the heat generated by the motor. An auxiliary fan, however, has many disadvantages.
One disadvantage is that the auxiliary fan increases the size or height of the motor assembly thereby preventing the streamlining of the motor assembly and the associated furnace within which the motor assembly is used. Another disadvantage is that the use of an auxiliary fan produces an additional load on the motor which can reduce the overall motor efficiency and increase the energy consumption of the furnace in which is it used. Furthermore, the use of an auxiliary fan increases the cost of manufacturing the draft inducing fan. Another disadvantage is that the auxiliary fan can generate additional noise which may require the furnace within which it is used to incorporate additional sound deadening techniques. Finally, because the motor is typically used in a vestibule, the airflow of the auxiliary fan is channeled into the vestibule thereby contributing to the elevated temperature of the vestibule and the associated components residing therein.
Therefore, it is an object of the present invention to provide an apparatus and method for cooling the motor that eliminates the need for an auxiliary fan.
The present invention overcomes shortcomings of prior art furnaces that use an auxiliary fan attached to the motor to cool the motor driving the draft inducing fan by providing a furnace that cools the motor with the flow of air induced by the draft inducing fan. By eliminating the need for an auxiliary fan, the present invention allows for the motor and fan assembly to be more compact and streamlined than the prior art motor, fan and auxiliary fan assemblies. Additionally, the present invention reduces the overall cost of providing a means to cool the motor while reducing the noise associated with cooling the motor with only a minimal load being placed on the motor.
In general, the furnace of the present invention is comprised of a motor which resides in a housing having at least one inlet and at least one outlet. A fan is driven by the motor and resides in a fan housing. The fan housing is operatively connected to and communicates with the motor housing and is configured and adapted to cause a flow of air to flow through the motor housing prior to entering the fan housing, thereby cooling the motor.
More specifically, the furnace is comprised of a motor in a motor housing having at least one inlet and at least one outlet. A combustion chamber has at least one inlet and an outlet with the at least one combustion chamber inlet being operatively connected to and communicating with the at least one motor housing outlet. A heat exchanger has an inlet and an outlet with the heat exchanger inlet being operatively connected to and communicating with the combustion chamber outlet. A fan driven by the motor resides in a fan housing and the fan housing has an inlet and an outlet. The heat exchanger outlet is operatively connected to and communicates with the fan housing inlet. The fan causes a flow of air to flow into the motor housing through the at least one motor housing inlet, around the motor, and exit the motor housing through the at least one motor housing outlet. The flow of air then flows into the combustion chamber through the at least one combustion chamber inlet, through the combustion chamber, and exits the combustion chamber through the combustion chamber outlet. The flow of air then flows into the heat exchanger through the heat exchanger inlet, through the heat exchanger, and exits the heat exchanger through the heat exchanger outlet. The flow of air then flows into the fan housing through the fan housing inlet and exits the fan housing through the fan housing outlet. The flow of air cools the motor as it flows through the motor housing and around the motor without the need for an auxiliary fan.
In another embodiment of the invention, the furnace is provided with a main blower in an inlet plenum of the furnace for circulating temperature controlled air through the furnace and an inducer fan for circulating combustion gases through the furnace that heat the circulated temperature controlled air. The inducer motor for driving the inducer fan is provided with a motor housing that defines a hollow interior of the motor housing that surrounds the motor. The motor housing is placed in communication with the inlet plenum. During operation of the main blower, cooling air is drawn through the interior of the inducer fan motor housing and into the inlet plenum of the furnace. The flow of air cools the inducer motor as it flows through the motor housing and around the motor without the need for an auxiliary fan on the inducer motor.